To achieve maximum output in internal combustion engines, turbochargers of the internal combustion engines are operated very close to their thermal limit. To monitor the exhaust temperature (hereinafter also referred to as T3), an exhaust gas temperature sensor may be used to vary combustion parameters of the internal combustion engine if the turbocharger is at risk of overheating.
The disadvantage of the aforementioned method is that the exhaust gas temperature sensor has a significant delay, and therefore reliable protection of the turbocharger through these means may be ensured only to a limited extent.
The use of a lambda sensor, which is present in any case, to limit the exhaust gas temperature, is also known from the related art. The lambda value measured by the lambda sensor may be used as a reference point for the exhaust gas temperature. The advantage of this method is that the lambda sensor is highly dynamic, i.e., it is suitable for carrying out lambda value measurements in rapid succession. However, the disadvantage is that the exhaust gas temperature is only imprecisely ascertainable from the lambda value, since this temperature is also dependent on other influencing factors, so that the temperature estimate using the lambda value has a tolerance of approximately +/−50 K. Such a high tolerance is unsatisfactory.